So far I have only had success for text only support using Pidgin with the SIPE plugin. I'm looking into SIP Communicator (which is java based and runs on all platforms) it does have some VOIP and Video support, but I have not been able to get it to connect to my company's OCS SIP server.
For Pidgin, get at least version 2.6.6 and install Pidgin-SIPE plugin version 1.8.0-1ubuntu1
- Create a new account, selecting the "Office Communicator" protocol.
- username is your corporate email address (email@example.com).
- login is [DOMAIN][Active Directory user name].
- password is your AD password.
it should detect your sip server automatically, however if not my best guess would be sip.yourdomain.com on port 5061
On my company's network it will only run if you disable the proxy.